N-vinyl-2-oxazolidinones as reactive diluents in actinic radiation curable coatings

ABSTRACT

An actinically curable composition containing (1) an oligomer having a molecular weight within the range of from about 200 to about 3000 and which is end capped with reactive functional groups to provide sites for free radical polymerization by actinic radiation and (2) as a reactive diluent, an N-vinyl-2-oxazolidinone in which the number 4 and 5 carbon atoms each have two constituents which are all independently selected from hydrogen and alkyl radicals having from 1 to 4 carbon atoms.

CROSS REFERENCE TO A RELATED APPLICATION

This application is a division of application Ser. No. 753,089, filed onJuly 9, 1985, now U.S. Pat. No. 4,639,472, which is acontinuation-in-part of application Ser. No. 682,450, filed on Dec. 17,1984, and which is now abandoned.

BACKGROUND OF THE INVENTION

Coating compositions which are curable under the influence of actinicradiation, e.g. ultra violet light, electron beam and the like, are wellknown. These coatings, generally contain, as the main characterizingcomponent, oligomers which are end capped with functional groups. Thesefunctional groups provide sites for actinic radiation initiated freeradical polymerization. Exemplary of some of these oligomers are thosewhich are end-capped with acrylate or methacrylate groups and which havea polyester, urethane, epoxy, polyether or acrylic backbone.

It has been found that while the oligomers used in the coatingcompositions contribute many useful characteristics thereto, they allsuffer one serious drawback. i.e., they are too viscous to insureconvenient, high fidelity application to a substrate. The oligomerviscosity can be lowered by diluting it with one or more solvents.Useful solvents are methyl ethyl ketone, ethyl acetate, xylene, toluene,acetone and the like. While solvents do reduce the viscosity of theoligomer their use is not widely acceptable as the solvent must beremoved from the cured coating thereby adding additional expense to thetotal curing process.

As an alternative to using solvents, the coating industry has turned tousing reactive diluents in admixture with the oligomer. The reactivediluent reacts with the oligomer during curing and becomes a part of thecured coating. No removal is needed. Exemplary of such diluents arestyrene, vinyl toluene, methyl acrylate, butyl acrylate, propylmethacrylate etc. While these diluents perform their viscosity loweringfunction in a manner preferred to that of solvents, they are generallyquite toxic. Great care and special safety equipment are required byworkers who apply coating compositions containing such diluents. Inresponse to this toxicity problem the coating industry is now movingtowards the selection of reactive diluents which are satisfactory intheir viscosity reducing function and which are relatively free fromknown toxic effect. Such a reactive diluent is the highly toutedcompound, N-vinyl-pyrrolidone. This pyrrolidone, however, has a strongodor which makes it use disagreeable to those applying the coatingcomposition.

It is therefore an object of this invention to provide an actinicallycurable, oligomer based, coating composition which; uses a reactivediluent, is relatively free of known toxic effect and which does nothave a strong odor. It is a further object of the invention to provide acured coating from such a composition.

THE INVENTION

This invention relates to an actinic radiation curable composition. Thecomposition comprises (a) an oligomer having a molecular weight withinthe range of from about 200 to 3000 and which is end-capped withreactive functional groups to provide sites for free radicalpolymerization by actinic radiation and (b), as an reactive diluent, aN-vinyl-2-oxazolidinone having the formula, ##STR1## wherein each "X" isindependently selected from the group consisting of hydrogen and alkylradicals. The alkyl radicals will contain from 1 to about 4 carbonatoms.

This invention also relates to the coating realized from actinicallycuring the just described composition. This coating will contain apolymer, which is at least in part, a polymerization product of theoligomer and the N-vinyl-2-oxazolidinone. It has been found that thecoatings of this invention have enhanced oxygen permeability.

Further, this invention relates to a process for curing the abovedescribed oligomer by co-mixing with it, as a reactive diluent, theabove described N-vinyl-2-oxazolidinone. The resultant mixture is thenexposed to actinic radiation to achieve a coating which is dry andsolid.

The oligomers used in the compositions, coatings and processes of thisinvention are preferrably end-capped with acrylate groups, methacrylategroups, vinyl ether groups, allyl ether groups or any combinationsthereof. Due to their ease of polymerization, acrylate and methacrylateend-capped oligomers are most preferred. These preferred oligomers canbe represented by the formula: ##STR2## in which R₁ is independentlyselected from hydrogen and methyl and in which R₂ represents thebackbone of the oligomer and is substantially comprised of polyesterunits, urethane units, epoxy units, polyether units or acrylic units.The selection of the particular units to form the backbone will bedependent in part upon the physical properties desired for the resultantcured coating.

Oligomers of acrylated polyesters have low viscosities and the coatingsproduced therefrom have good weatherability. These oligomers aremanufactured by condensation reactions. For example, a particularlyuseful acrylated polyester is the one synthesized from acrylic acid anda 1,6-hexanediol/adipic acid polyester. Maleic anhyrdride or some otherunsaturated dibasic acid can be used to replace a portion of the adipicacid. It is also possible to use a hydroxy functional acrylate or adicarboxy functional polyester.

Acrylated urethane oligomers are used to make coatings havingexceptional abrasion resistance and flexibility. These coatings alsopossess toughness, hardness, and chemical resistance. A wide choice ofpolyethers, polyester diols and polyols can be reacted with a variety ofaliphatic and aromatic isocyanates to synthesize the oligomer backbone,which is then end-capped with a hydroxyalkyl acrylate. Other examples ofpolyester urethanes are the polycaprolactone polyols reacted withdiisocyanates and end-capped with 2-hydroxypropyl acrylate. Hydroxy-richalkyds or polyesters which have been reacted with diisocyanates can alsobe end-capped with hydroxyalkyl acrylates to form ultra-violet lightcurable oligomers.

Coatings based on acrylated epoxy oligomers have excellent adhesion,penetration, hardness, and chemical resistance. Exemplary of sucholigomers are acrylated epoxidized soybean oils and bisphenol A basedepoxy diacrylates.

Acrylated polyether oligomer based coatings possess abrasion resistance,flexibility, and toughness. Many oligomer variations are available bychanging the polyether polyol functionality from 2 to 6 and by varyingthe molecular weight. Formation of polyether acrylate is achieved by thepolycondensation of propylene glycol to a polypropylene glycol ether andend-capping such with acrylic acid.

Acrylated acrylics are especially useful for outdoor applications. Oneexample, is the acrylated acrylic produced by the acrylation of aglycidyl methacrylate terpolymer with acrylic acid.

As before mentioned, the N-vinyl-2-oxazolidinones of this invention have"X" constituents which are independently selected from the groupconsisting of hydrogen and alkyl radicals in which the alkyl radicalcontains from 1 to about 4 carbon atoms. Exemplary of suchoxazolidinones are: N-vinyl-5-methyl-2-oxazolidinone;N-vinyl-2-oxazolidinone; N-vinyl-4-methyl-2-oxazolidinone;N-vinyl-5-ethyl-4-methyl-2-oxazolidinone;N-vinyl-5-butyl-2-oxazolidinone; N-vinyl-4-propyl-2-oxazolidinone; andN-vinyl-4,4-diethyl-5,5-dimethyl-2-oxazolidinone. The preferredoxazolidinones of this invention are those in which the "X" constituentis chosen so that three of the constituent members are hydrogen with theremaining constituent member being an alkyl radical. For these compoundsit is preferred that the alkyl radicals be methyl or ethyl radicals. Aparticularly useful and most highly preferred oxazolidinone of thisinvention is N-vinyl-5-methyl-2-oxazolidinone.

The N-vinyl-2-oxazolidinones of this invention and the processes forproducing same are disclosed in U.S. Pat. Nos. 2,818,362 and 2,919,279,which disclosures are incorporated herein by reference.

The respective amounts of the oligomer and the N-vinyl-2-oxazolidinonesselected can vary widely so long as the properties of the resultantcured coatings are not adversely affected. Generally the oligomer andthe selected N-vinyl-2-oxazolidinone are present, respectively, in aratio by weight within the range of from about 1:5 to about 10:1 andpreferrably within the range of from about 2:3 to about 3:7. At higherratios, e.g., those rich in oligomer, the uncured coating compositiontends to have too high a viscosity. This high viscosity makes itdifficult to apply the uncured coating composition to the substrate. Atlower ratios the resultant cured coating composition tends to be toohard and inflexible.

If the actinic radiation curing of the coating composition is to beachieved with ultra-violet light, a photoinitiator and/or aphotosensitizer are used in the composition. Such initiators andsensitizers are useful in controlling and making more efficient thepolymerization reaction which is characteristic of the curing process.Photoinitiators are compounds which absorb photons and thereby obtainenergy to form radical pairs, at least one of which is available toinitiate addition polymerization in the well-known manner.Photosensitizers are compounds which are good absorbers of photons, butwhich are themselves poor photoinitiators. They absorb photons toproduce excited molecules which then interact with a second compound toproduce free radicals suitable for initiation of additionpolymerization. The second compound may be a monomer, a polymer or anadded initiator.

Most of the well known photoinitiators may be used in the coatingcompositions of the invention. Suitable initiators are vicinalketaldonyl compounds (i.e. compounds containing a ketone group and analdehyde group), for example, diacetyl; 2,3-pentanedione;2,3-octanedione; 1-phenyl-1,2-butanedione;2,2-dimethyl-4-phenyl-3,4-butanedione; phenyl-glyoxal; anddiphenyltriketone. Aromatic diketones, e.g., anthraquinone andacryloins, such as, benzoin are also useful initiators. Other suitableinitiators are pivaloin acryloin ethers, such as, benzoin-methyl-ether,benzoin-ethyl-ether, benzoin-butyl-ether, benzoin-isobutyl-ether andbenzoin-phenyl-ether. Alphal-hydrocarbon substituted aromatic acyloinsmay also be used, including alpha-methyl-methyl-benzoin,alpha-alkyl-benzoin (as in U.S. Pat. No. 2,722,512) and phenylbenzoin.Still, other initiators are diaryl ketones, e.g., benzophenone anddinaphthyl ketone, and organic disulfides, such as, diphenyldisulfide.The photoinitiator can also be used with synergistic agents, e.g., atertiary amine, to enhance the conversion of photo-absorbed energy topolymerization initiating free radicals. Preferred initiators are:alpha, alpha-diethoxyacetophenone; alpha,alpha-demethoxy-alpha-phenylacetophenone, dimethoxyphenylacetophenone,and a benzoin ether such as Vicure 10 which is available from StaufferChemical Co. The photoinitiator is present in the coating composition inan amount sufficient to initiate the desired polymerization under theinfluence of the amount of actinic light energy absorbed. If theconcentration of photoinitiator is too high, curing may occur only atthe surface. However, if the photoinitiator concentration is too low theexposure time needed to achieve curing may be too long from a economicalstand point. The coating composition generally contains from 0.01 to 10weight percent of photoinitiator based on the weight of the coatingcomposition.

Exemplary of photosensitizers which can be used alone or in combinationwith a photoinitiator are: benzophenone; 4,4 bis(N,N-dimethylamino)benzophenone; 9,10-phenthrenequinoine; xanthone; thioxanthone;2-chlorothixanthone; benzil; and 9,10-anthraquinone. The amount ofphotosensitizer used in the coating composition is best determinedempirically and will be dependent upon the curing time desired, theavailable actinic light energy and the chemical and physical nature ofthe components making up the composition.

The coating compositions of this invention can also contain otherconventional additives such as; addition polymerization inhibitors,surfactants, flow control and leveling agents, organic and inorganicdyestuffs and pigments, fillers, plasticizers, lubricants, andreinforcing agents.

Generally the subject coating compositions are formulated by adding theselected N-vinyl-2-oxazolidinone reactive diluent to the oligomer.However, the oligomer can be added to the reactive diluent. After suchaddition, blending or stirring of the mixture can be utilized to insurehomogenity. The addition of the before mentioned additives can also beperformed contemporaneously during the oligomer/reactive diluentaddition.

The coating composition of this invention is generally applied to asubstrate as a film having a thickness within the range of from 0.1 toabout 20 mils. However, thicker coatings, i.e., up to a 1000 mils thickare possible. To prevent discoloration of the resultant cured coating itis preferred that the curing occur under an inert atmosphere such asthat provided by nitrogen. The coating composition may be applied in anyconventional manner such as by spraying, printing, brushing, dipping,roll coating and the like. The substrates which may be coated with thecomposition may vary widely in their properties. Organic substrates suchas wood, fiber board, particle board, composition board, paper andcardboard may be used. Various polymers, such as polyesters, polyamides,cured phenolic resins, cured aminoplasts, acrylics, polyurethanes andrubber are also suitable. Inorganic substrates are exemplified by glass,quartz and ceramic materials. Many metallic substrates may be coated.Exemplary metallic substrates are iron, steel, stainless steel, copper,brass, bronze, aluminium, magnesium, titanium, nickel, chromium, zincand various alloys.

As used herein the term actinic radiation refers to any radiation sourcewhich will produce free radicals and induce addition polymerization ofvinyl bonds. The actinic radiation is most conveniently provided byultra-violet light or by electron beam. When ultra-violet light isutilized as the actinic radiation, the before described photoinitiatorsand photosensitizers are used. When electron beam radiation is utilized,due to its higher energy level, no photoinitiator or photosensitizer isnecessary.

Any suitable source which emits ultra-violet light may be used forultra-violet actinic radiation. Suitable sources are mercury arcs,carbon arcs, low pressure mercury lamps, medium pressure mercury lamps,high pressure mercury lamps, swirl-flow plasma arcs, ultra-violet lightemitting diodes and ultra-violet light emitting lasers. Particularlypreferred ultra-violet light emitting lamps are the medium and highpressure mercury vapor type.

A preferred electron beam system uses a wide curtain of electrons whichare directed from a linear cathode. The curtain of electrons from thecathode gun is accelerated to sufficient velocity by a high KVpotential, e.g. 200 KV, and emerges from the chamber through a foilwindow onto the coated substrate. Electron beam curing of the coatingcomposition is generally achieved at less than 5M rads and generally at2M rads. Curing at greater than 8M rads is deemed unacceptable becauseof the high cost.

The cured coatings of this invention exibit enhanced oxygenpermeability--indeed some compositions have been found to have an oxygenpermeability at 23.5° C. of 9320 cc-mil/m² -day-atm O₂ as measured byASTM D 3985-81. Coating compositions formulated in accordance with theteachings herein, but without the selected oxazolidinone, had oxygenpermeabilities of only about 2500 cc/mils/m² -day-atm O₂ using the sameASTM procedure.

The coatings formed by the coating compositions of the invention areuseful in formulating printing inks, providing protective coatings onvarious substrates, imparting gloss to printed substrates and any of theother well known applications for actinically cured coatingcompositions.

The inventions herein described are further illustrated by the followingnon-limiting examples. In the examples some compounds, compositions andmaterials are identified by their manufacturer's designated name. Theyare as follows:

    ______________________________________                                        Compound,                                                                     Composition                Manufacturer or                                    Material    Function/Description                                                                         Distributor                                        ______________________________________                                        CELRAD 6700 urethane acrylate                                                                            Celanese Chemical                                              oligomer       Co., Dallas, TX                                    CELRAD 3700 epoxy acrylate Celanese Chemical                                              oligomer       Co., Dallas, TX                                    IRGACURE 651                                                                              photoinitator  Ciba Giegy, Corp.                                                             Hawthorne, N.Y.                                    IRGACURE 184                                                                              photoinitiator Ciba Giegy, Corp.                                                             Hawthorne, N.Y.                                    UVITHANE 783                                                                              polyester urethane                                                                           Morton Thickol,                                                acrylate oligomer                                                                            Inc., Specialty                                                               Chemical Div.                                                                 Trenton, N.J.                                      BONDERITE 37                                                                              treatment applied                                                                            Parker Chemical                                                to cold rolled Co., Morenci,                                                  steel test panel                                                                             Michigan                                           ______________________________________                                    

Various properties of the cured coatings in the examples were measuredas follows:

    ______________________________________                                        Test                Procedure                                                 ______________________________________                                        Pencil Hardness     ASTM D 3363                                               Cross Hatch Adhesion                                                                              ASTM D 3359                                               Mandrel             ASTM D 3111                                                                   (slightly modified)                                       Solvent Resistance  Acetone on cloth                                                              double rub over                                                               coating, 100                                                                  repetitions.                                              ______________________________________                                    

EXAMPLE I

A thoroughly mixed composition 21.9 g of CELRAD 6700, 14.6 gN-vinyl-5-methyl-2-oxazolidinone (93% pure) and 0.9 g IRGACURE 651 wasprepared. A 1 mil thick film of this composition was applied to aBONDERITE 37 treated test panel with a 1/2" wire wound rod. The thuscoated test panel was then exposed, in air, to an ultra violet lightfrom a 250 watt Hanovia medium pressure mercury vapor lamp until thecoating was observed to have been cured. The cured coating was clear,glossy and had a Pencil Hardness of 2 H.

EXAMPLE II

The procedure of Example I was repeated except that the compositionadditionally contained 3 g of trimethylolpropane triacrylate (toincrease the cross link density of the cured coating.) The resultantcured coating was hard, glossy and had a Pencil Hardness of 5 H.

EXAMPLE III

A well mixed composition containing 59.6 g UVITHANE 783, 12.8 gN-vinyl-5-methyl-2-oxazolidinone (93% pure), 12.8 g diethylenegylcolmonoethylether acrylate (an additional diluent) and 1.76 g IRGACURE 651was prepared. This composition was applied as a 1 mil thick film by a1/2" wire wound rod to BONDERITE 37 treated test panels. The thus coatedpanels were cured while exposed to air and in an Ashdee UV Oven having a1-200 watt mercury vapor lamp. The Ashdee oven provides a variable speedconveyer on which the test panels are placed to carry them under the UVlamp. (The Ashdee UV Oven is marketed by Ashdee Division of George Koch& Sons, Inc. of Evansville, Ind.). The following table summarizes thecuring parameters and the results.

    ______________________________________                                        Panel                         Pencil                                                                              1/4"  Solvent                             Test  Lamp    Conveyor  No. of                                                                              Hard- Man-  Resis-                              No.   Power   Speed     Passes                                                                              ness  drel  tance                               ______________________________________                                        1     full     42 ft/min                                                                              1     2B    Passed                                                                              Good                                2     full     60 ft/min                                                                              1     2B    Passed                                                                              Good                                3     full    131 ft/min                                                                              1     2B    Passed                                                                              Good                                4     full    131 ft/min                                                                              3     2B    Passed                                                                              Good                                ______________________________________                                    

EXAMPLE IV

The procedure of Example III was repeated except that the conveyor beltspeed was changed and the composition contained 16.0 g UVITHANE 783,3.44 g diethyleneglycol monoethylether acrylate, (an additionaldiluent), 3.43 g N-vinyl-5-methyl-2oxazolidinone and 0.45 g IRGACURE651. The following table reports the parameters used and the testresults.

    ______________________________________                                                             Conveyor  No. of Pencil                                  Test Panel No.                                                                          Lamp Power Speed     Passes Hardness                                ______________________________________                                        1         full        52 ft/min                                                                              1      HB                                      2         full       211 ft/min                                                                              1      HB                                      ______________________________________                                    

EXAMPLE V

A base composition containing 53 weight % CELRAD 3700, 31 weight %trimethylolpropane triacrylate, 10.7 weight % hexanediol diacrylate (toincrease cross link density of the coating) and 5 weight %N-vinyl-5-methyl-2-oxazolidinone was prepared.

To 10 g of this base composition was added 2 g IRGACURE 651. Theresultant admixture was applied to yield a 1 mil thick coat on aBONDERITE 37 treated test panel by the use of a 1/2" wire round bar. Thecoated test panel was passed through an Ashdee UV oven 3 times at therate of 100 ft/min under two 200 watt/in medium pressure mercury lamps.The resultant curing occurred in air and the coating had a 70% CrossHatch Adhesion. The coating failed the 1 inch Mandrel test and had aPencil Hardness of 8 H. Solvent Resistance was good as observed after100 double rubs with acetone.

EXAMPLE VI

The base composition of Example V was mixed with 0.2 g IRGACURE 184 andthe procedure of Example V was followed. The resultant cured coating hada 12% Cross Hatch Adhesion, a Pencil Hardness of 8H and exhibited goodSolvent Resistance after at least 100 double rubs with acetone. The 1inch Mandrel test was failed.

The foregoing examples illustrate the good physical characteristics ofthe coatings of this invention. Also, the curing times for thecompositions are short thus showing high process efficiency. (Generallycuring rates greater than 20 ft/min/lamp are needed for commerciallyacceptable compositions.)

We claim:
 1. An actinic radiation curable composition whichcomprises:(a) an oligomer having a molecular weight within the range offrom about 200 to about 3000 which is substantially comprised ofpolyether units and which is end capped with reactive functional groupsto provide sites for free radical polymerization by actinic radiation;and (b) as a reactive diluent, an N-vinyl-2-oxazolidinone having theformula, ##STR3## wherein each X is independently selected from thegroup consisting of hydrogen and alkyl radicals, said alkyl radicalscontaining from 1 to about 4 carbon atoms.
 2. The composition of claim 1wherein said oligomer is end capped with acrylate groups, methacrylategroups, vinyl ether groups, allyl ether groups or any combinationthereof.
 3. The composition of claim 1 wherein said oligomer is endcapped with acrylate groups.
 4. The composition of claim 1 wherein eachX is selected so that three are said hydrogen and one is said alkylradical.
 5. The composition of claim 4 wherein said oligomers areend-capped with acrylate groups, methacrylate groups, vinyl ethergroups, allyl ether groups or any combination thereof.
 6. Thecomposition of claim 4 wherein said oligomer is end-capped with acrylategroups.
 7. The composition of claim 6 wherein saidN-vinyl-2-oxazolidinone is N-vinyl-5methyl-2-oxazolidinone.
 8. Thecomposition of claim 1 wherein said N-vinyl-2-oxazolidinone isN-vinyl-5-methyl-2-oxazolidinone.
 9. The composition of claim 1 whereinthe weight ratio of said oligomer to said N-vinyl-2-oxazolidinone isbetween about 1:5 and about 10:1.
 10. The composition of claim 4 whereinthe weight ratio of said oligomer to said N-vinyl-2-oxazolidinone isbetween about 1:5 and about 10:1.
 11. The composition of claim 7 whereinthe weight ratio of said oligomer to said N-vinyl-2-oxazolidinone isbetween about 1:5 and about 10:1.
 12. A highly oxygen permeableactinically cured coating which comprises a polymer including apolymerization product of:(a) an oligomer having a molecular weightwithin the range of from about 200 to about 3000 which is substantiallycomprised of polyether units and which is end capped with functionalgroups to provide sites for free radical polymerization by actinicradiation; and (b) as a reactive diluent, an N-vinyl-2-oxazolidinonehaving the formula, ##STR4## wherein each X is independently selectedfrom the group consisting of hydrogen and alkyl radicals, said alkylradicals containing from 1 to about 4 carbon atoms.
 13. The process ofclaim 1 wherein said polyether units are polypropylene glycol ether andsaid oligomer is end capped with functional groups selected from thegroup consisting of acrylate groups, methacrylate groups, and mixturesthereof.